全文获取类型
收费全文 | 2148篇 |
免费 | 62篇 |
国内免费 | 14篇 |
专业分类
化学 | 1608篇 |
晶体学 | 8篇 |
力学 | 47篇 |
数学 | 166篇 |
物理学 | 395篇 |
出版年
2022年 | 17篇 |
2021年 | 19篇 |
2020年 | 27篇 |
2019年 | 35篇 |
2018年 | 23篇 |
2017年 | 16篇 |
2016年 | 56篇 |
2015年 | 50篇 |
2014年 | 48篇 |
2013年 | 133篇 |
2012年 | 85篇 |
2011年 | 138篇 |
2010年 | 66篇 |
2009年 | 54篇 |
2008年 | 122篇 |
2007年 | 119篇 |
2006年 | 96篇 |
2005年 | 107篇 |
2004年 | 85篇 |
2003年 | 75篇 |
2002年 | 74篇 |
2001年 | 62篇 |
2000年 | 49篇 |
1999年 | 36篇 |
1998年 | 35篇 |
1997年 | 25篇 |
1996年 | 33篇 |
1995年 | 28篇 |
1994年 | 36篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 18篇 |
1980年 | 21篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 16篇 |
1975年 | 12篇 |
1974年 | 14篇 |
1973年 | 19篇 |
排序方式: 共有2224条查询结果,搜索用时 15 毫秒
31.
Frabetti PL Cheung HW Cumalat JP Dallapiccola C Ginkel JF Greene SV Johns WE Nehring MS Butler JN Cihangir S Gaines I Garren L Garbincius PH Gourlay SA Harding DJ Kasper P Kreymer A Lebrun P Shukla S Bianco S Fabbri FL Sarwar S Zallo A Culbertson R Gardner RW Greene R Wiss J Alimonti G Bellini G Caccianiga B Cinquini L Di Corato M Giammarchi M Inzani P Leveraro F Malvezzi S Menasce D Meroni E Moroni L Pedrini D Perasso L Sala A Sala S Torretta D Vittone M Buchholz D Claes D Gobbi B O'Reilly B 《Physical review letters》1993,70(10):1381-1384
32.
Frabetti PL Cheung HW Cumalat JP Dallapiccola C Ginkel JF Greene SV Johns WE Nehring MS Butler JN Cihangir S Gaines I Garren L Garbincius PH Gourlay SA Harding DJ Kasper P Kreymer A Lebrun P Shukla S Bianco S Fabbri FL Sarwar S Zallo A Culbertson R Gardner RW Greene R Wiss J Alimonti G Bellini G Caccianiga B Cinquini L Di Corato M Giammarchi M Inzani P Leveraro F Malvezzi S Menasce D Meroni E Moroni L Pedrini D Perasso L Sala A Sala S Toretta D Vittone M Buchholz D Claes D Gobbi B O'Reilly B 《Physical review letters》1993,70(12):1755-1758
33.
Powell SA Tenenbaum JM Woerpel KA 《Journal of the American Chemical Society》2002,124(43):12648-12649
We have developed a route for the stereoselective synthesis of 1-oxa-2,2-(dimesityl)silacyclopentane acetals, intermediates in the synthesis of highly functionalized 1,3-diols. This route involves a diastereoselective conjugate addition reaction of a hydrosilyl anion, a subsequent diastereoselective enolate alkylation, and a fluoride-catalyzed intramolecular hydrosilylation reaction to afford the oxasilacyclopentane acetal. A highly selective nucleophilic substitution reaction, followed by oxidation of the C-Si bond, leads to the desired polyol. 相似文献
34.
35.
Koumi P Green HE Hartley S Jordan D Lahec S Livett RJ Tsang KW Ward DM 《Electrophoresis》2004,25(14):2227-2241
The demand for high-throughput DNA profiling has increased with the introduction of national DNA databases and has led to the development of automated methods of short tandem repeat (STR) profile production; however, a potential bottleneck still exists at the gel electrophoresis stage. Capillary electrophoresis sequencers capable of processing 96 samples with considerably reduced manual intervention are now available. In this paper, we compare the ABI Prism 377 slab-gel sequencer currently used by the Forensic Science Service with three leading capillary array electrophoresis instruments: the ABI Prism 3700, the Amersham MegaBACE 1000 and the 16-capillary ABI Prism 3100. We describe the experiments used to evaluate and validate these platforms for forensic use with the STR multiplex Ampf/STR SGMplus [1, 2], along with comparative data from the ABI Prism 377 sequencer. 相似文献
36.
G. Kennedy 《Journal of Radioanalytical and Nuclear Chemistry》1995,193(2):239-245
A method has been developed for the correction of counting losses in NAA for the case of a mixture of short-lived radionuclides. It is applicable to systems with Ge detectors and Wilkinson or successive approximation ADC's and will correct losses from pulse pileup and ADC dead time up to 90%. The losses are modeled as a constant plus time-dependent terms expressed as a fourth order polynomial function of the count rates of the short-lived radionuclides. The correction factors are calculated iteratively using the peak areas of the short-lived radionuclides in the spectrum and the average losses as given by the difference between the live time and true time clocks of the MCA. To calibrate the system a measurement is performed for each short-lived nuclide. In a test where the dead time varied from 70% at the start of the measurement to 13% at the end, the measured activities were corrected with an accuracy of 1%. 相似文献
37.
38.
Despite the popularity of boron and silicon allylation reagents in stereocontrolled synthesis, they suffer from a number of inherent limitations that have slowed down their development as synthetic tools for nucleophilic additions to carbonyl compounds and imine derivatives. These limitations are the low reactivity and diastereoselectivity of allyl trialkylsilane reagents, and the lack of catalytic systems for the activation and substoichiometric control of enantioselectivity in the additions of allyl boron reagents. To develop more efficient and general methods for the control of absolute stereochemistry in the resulting homoallylic alcohols, new approaches aimed at solving the problem of activation of allylic boron and silicon reagents are needed. This Minireview describes a number of recent approaches that have been devised to address this problem. 相似文献
39.
Using magnetic and magnetoelectric (ME) powder susceptibility measurements, the low temperature magnetic properties of antiferromagnetic UCrO4 and NdCrTiO5 have been studied. Their Néel temperatures TN are 44.5 and 20.5°K, respectively, the Cr3+ spin systems of both materials ordering cooperatively at TN. Below TN, the U5+ and Nd3+ moments are polarized due to their exchange interaction with the ordered Cr3+ spins. It is argued that, for both compounds, each of the two spin systems contributes to the ME susceptibilities. They are thus the first known ME materials possessing two distinct magnetic sublattices. The effective magnetic moments calculated from the magnetic susceptibilities are in good agreement with those previously reported by neutron diffraction studies. 相似文献
40.
Argouarch G Stones G Gibson CL Kennedy AR Sherrington DC 《Organic & biomolecular chemistry》2003,1(24):4408-4417
Three chiral 2,6-disubstituted tri-N-methyl azamacrocycles have been prepared by modular methods. These macrocycles were accessed from three chiral 1,4,7-triazaheptanes intermediates that were prepared by two independent routes. The first of these routes involved the benzylamine opening of chiral tosyl aziridines followed by debenzylation but was problematic on solubility grounds. A second, more effective, route was developed which avoided debenzylation by using ammonia in the nucleophilic opening of chiral tosyl aziridines. 相似文献